The present invention relates generally to exhaust nozzle structures for engines providing thrust by expulsion of gaseous products of combustion of fuel, and more particularly to a novel heat resistant, dual flow passage, short nozzle structure for a ramjet, rocket or turbojet powered missile.
In thrust producing engines such as ramjets, rockets and turbojets, the propulsive nozzle cooperates with the combustor of the engine to convert thermal energy of the gaseous combustion products of fuel burned in the combustor and entering the nozzle to directed kinetic energy (thrust) at the nozzle exit by the expansion of the gases upon discharge. The gross thrust developed by the nozzle is directly related to the exhaust velocity of the expanding gases, and in order to maximize the propulsive efficiency of the engine, the expansion process in the nozzle must be accomplished as efficiently as possible. Additionally, the range of a missile powered by a thrust producing engine is primarily dependent upon the amount of fuel carried aboard the missile. Therefore, for a given missile length, minimizing engine length may maximize fuel capacity and range of the missile.
In existing engines having thrust producing propulsive exhaust nozzles, conventional axisymmetric convergent/divergent nozzles have found widespread use. This nozzle configuration normally exhibits efficient design point performance, acceptable weight, performance and cost attributes, and established and accurate design analysis technology; disadvantages of the conventional configuration include excessive nozzle length and inefficient off design performance. One annular nozzle configuration having an axisymmetric certerbody inserted near the throat of a conventional convergent/divergent nozzle and defining a substantially annular exhaust flow passage has been suggested to overcome the aforesaid disadvantages. Centerbody nozzle configurations may include the types disclosed by or referenced in U.S. Pat. No. 3,940,067.
Proposed solutions to overcome certain of the aforesaid disadvantages also include the replacement of a traditional axisymmetric conical nozzle with a multiple flow area nozzle. To obtain good propulsive efficiency, the flow passages of such nozzles are separated by relatively thin webs which are directly exposed to severe heating by combustion gases. A conventional fabrication approach for these webs has consisted of applying insulating material to a metal skeleton. With this approach, however, propulsive efficiency degrades during operation due to dimensional changes in the webs defining the multiple flow passages, and engine operating time is substantially limited by the exposure time of the webs at the temperature of the combustion gases.
The present invention provides an improved nozzle structure of large diameter to length ratio in a dual exhaust flow, substantially fixed geometry, convergent/divergent configuration. The nozzle is defined by a double wedge shaped web disposed transversely of the throat of a conical nozzle and which divides the region defined by the walls of the nozzle into two symmetrical flow passageways. The web and wall components of the nozzle comprise of a composite material including carbon yarn reinforcements within a carbon matrix. A coating of pyrolytic graphite deposited on the exposed surfaces of the web and walls retards oxidation by the exhaust gases.
It is, therefore, a principal object of the present invention to provide an improved exhaust nozzle structure for an engine providing propulsive thrust to a vehicle by expulsion of gaseous products of fuel combustion.
It is a further object of the invention to provide an exhaust nozzle structure which is characterized by minimum length.
These and other objects of the present invention will become apparent as the detailed description of certain representative embodiments thereof proceeds.